QuickSwap and StellaSwap contest - dharma09's results

1.DEFAULT VALUE INITIALIZATION

PROBLEM

If a variable is not set/initialized, it is assumed to have the default value (0, false, 0x0 etc depending on the data type). Explicitly initializing it with its default value is an anti-pattern and wastes gas.

PROOF OF CONCEPT

Instances include: DataStorage.sol#L307

MITIGATION

 for (uint256 i; i < secondsAgos.length; ++i)

Caching the length in for loops

PROBLEM

In the context of a for-loop that iterates over an array, it costs less gas to cache the array's length in a variable and read from this variable rather than use the arrays .length property. Reading the .length property for on the array will cause a recalculation of the array's length on each iteration of the loop which is a more expensive operation than reading from a stack variable.

For example, the following code:

for (uint i; i < arr.length; ++i) {
        // ...
}

This extra costs can be avoided by caching the array length (in stack): should be changed to:

uint length = arr.length;
for (uint i; i < length; ++i) {
        // ...
}

INSTANCES

2.COMPARISONS: != IS MORE EFFICIENT THAN > IN REQUIRE (6 GAS LESS)

!= 0 costs less gas compared to > 0 for unsigned integers in require statements with the optimizer enabled (6 gas)

For uints the minimum value would be 0 and never a negative value. Since it cannot be a negative value, then the check > 0 is essentially checking that the value is not equal to 0 therefore >0 can be replaced with !=0 which saves gas.

While it may seem that > 0 is cheaper than !=, this is only true without the optimizer enabled and outside a require statement. If you enable the optimizer at 10k AND you’re in a require statement, this will save gas.

PROOF OF CONCEPT

Instances include: PriceMovementMath.sol#L52 PriceMovementMath.sol#L53

require(price != 0);
require(liquidity != 0);

AlgebraPool.sol#L224 AlgebraPool.sol#L434 AlgebraPool.sol#L454 AlgebraPool.sol#L454 AlgebraPool.sol#L454 AlgebraPool.sol#L454 AlgebraPool.sol#L454 AlgebraPool.sol#L454

3.Require statements including conditions with the && operator can be broken down in multiple require statements to save gas.

PROOF OF CONCEPT

Instances include: DataStorageOperator.sol#L46 changes:

require(_feeConfig.gamma1 != 0, 'Gammas must be > 0');
require(_feeConfig.gamma2 != 0, 'Gammas must be > 0');
require(_feeConfig.volumeGamma != 0, 'Gammas must be > 0');

AlgebraFactory.sol#L110

require(gamma1 != 0, 'Gammas must be > 0');
require(gamma2 != 0 , 'Gammas must be > 0');
require(volumeGamma != 0, 'Gammas must be > 0');

AlgebraPool.sol#L739 AlgebraPool.sol#L743

require(limitSqrtPrice < currentPrice, 'SPL');
require(limitSqrtPrice > TickMath.MIN_SQRT_RATIO, 'SPL');

AlgebraPool.sol#L953 AlgebraPool.sol#L968

require((communityFee0 <= Constants.MAX_COMMUNITY_FEE);
require(communityFee1 <= Constants.MAX_COMMUNITY_FEE));